Introduction to Genetic Analysis 637

Introduction to Genetic Analysis 637 - recessive alleles to...

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Unformatted text preview: recessive alleles to have frequencies much higher than those of partly dominant alleles, because the recessive al- leles are protected in heterozygotes. 19.6 Random events If a population consists of a finite number of individuals (as all real populations do) and if a given pair of parents has only a small number of offspring, then even in the absence of all selective forces, the frequency of a gene will not be exactly reproduced in the next generation, because of sampling error. If, in a population of 1000 in- dividuals, the frequency of a is 0.5 in one generation, then it may by chance be 0.493 or 0.505 in the next generation because of the chance production of slightly more or slightly fewer progeny of each genotype. In the second generation, there is another sampling error based on the new gene frequency, so the frequency of a may go from 0.505 to 0.511 or back to 0.498. This process of random fluctuation continues generation after genera- tion, with no force pushing the frequency back to its ini- tial state, because the population has no “genetic mem- ory” of its state many generations ago. Each generation is an independent event. This random change in allele fre- quencies is known as genetic drift....
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.

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